text:
How profitable is an airline shuttle flight between BOS and DCA on an A320?
I was computing the hypothetical profitability of commercial airline flights and it seems to be pretty extreme. For example, looking at the Boston-DCA shuttle, pro-rating all costs to the just the flight itself using conservative figures I came up with the following:
aircraft: A320
distance: 346 nautical miles
fuel usage: 6500 pounds
fuel: 3800
maintenance: 2000
crew: 1200
hangar: 900
insurance: 400
Total costs: 8,300
passenger count: 150
ticket charge: 200
Total revenue: 30,000
Based on these figures, profitability of this route seems to be about 350%, i.e., more than tripling your costs on every flight. Even if we allow for tickets of $100 each, it is still almost a 100% profit.
Am I missing something, or are these figures in the right ballpark?
THIS IS NOT A DUPLICATE OF long-haul flight costs. That post is for LONG HAUL flights. This is a shuttle. That post concerns a completely different aircraft with costs amortized ANNUALLY. This is post is about PER-FLIGHT profitability, not ANNUAL profitability.
ALSO: This post asks about PROFITABILITY on this route, not just costs. It includes REVENUE. I am not asking general profitability; I am asking about this calculation for profitability on the route in question using the aircraft in question (A320).

tickets prices fluctuate like mad, courtesy of the marketing department with first minute discounts, last-minute discounts group sales etc.

You need to include airport fees and several other related expenses. A new route initiation takes a lot of time, money and lobbying. A lot of regulations have to be maintained. Then you need to add executives', lawyers' and flight crew's salaries.

Your cost calculation doesn't include anything like infrastructure (ticketing, baggage, ground support, reservations) and other GA costs.

Additionally, your calculation doesn't include the amortization cost of the aircraft itself.

Also, the revenue estimate is probably way off. It seems very unlikely that the airline is averaging $200/seat for a single 350 nm flight segment. I usually get round-trips with each way being twice that distance for between $200 and $300 USD. Finally, even if the figures were correct, 30,000 - 8,300 = 21,700 which is 260% of 8,300, not 350%.

Your estimate of insurance seems way low if you are including liability insurance as well as hull coverage.  and advertising.

I think that profitability is a lot more difficult to estimate than costs: the price of jet-A is public, but an airline may offer dozens of different seat prices for one flight. And there's cargo too, which could bring a lot of money or just a little. But in any case, the Economist said that in 2012 airlines worldwide made a profit of $4 per customer carried, so your calculation seems very optimistic (unless BOS-DCA is a very profitable outlier).

@Pondlife The question is not about general profitability. The question is about the calculation for this one particular route and aircraft type.

@TylerDurden DCA has particularly expensive airport and security costs, because it lies inside the presidential TFR

Also missing the load factor... I highly doubt all flights would be 100% full.


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Can someone identify this scrapped high-wing plane?

I consider myself to be a decent aircraft identifier, and when I saw this plane when exploring an aircraft graveyard, I was not able to identify it. I took a pic and showed it to several aviation Facebook groups, and nobody was able to identify it. Maybe we’re just being dumb and it’s something simple, but can somebody help? Thanks!

Where did you see this?

The N-number is still there on the tail you could use that in one of the registration databases.

@ratchetfreak - partially there. Can you make it out?

@Jamiec Not in this picture but the original non-scaled image may have it more readable.

Cpt Reynolds It was found in Discount Aircraft Salvage, an Aircraft Graveyard is Deer Park, WA.

If that is N3380G, I saw it at EAA Airventure Oshkosh in 2001.  It was a Mexican built model, not Italian.  I have a pic of the dataplate showing Lockheed-Azcarate S.A., AeroGuayin, Model LASA-60, S/N 1010.

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What aircraft is this twin prop?
Sorry it's the only picture I have.

Welcome to Aviation.SE. I am going to edit this question for you, but next time please try to use a more professional language.

The aircraft is almost certainly a Beechcraft B200 or B200C King Air, with a combined Cargo-and-Airstair Door, as can be seen in these photos:

(source)

(source)
The airstair door is essentially a door-within-a-door and opens downwards as usual:

(source)
The larger cargo door opens upwards:

(source)

I know that two of the photos have the source printed on them but please add your sources for your images.

Good catch noticing the cargo door.

Looks like a Beechcraft Super King Air
Judging by the amount of windows it is not the regular King Air
source

Please include the source of your image

What is a "regular" King Air? Are you referring to the 90?

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Why don't most military transports use modern commercial engines?
Why don't most military transports use modern commercial engines?
More specifically planes like C-17, the Antonov's use older less powerful engines while modern efficient and powerful engines are available in the commercial sector.

mainly because their missions are different (cruise and landing speed constraints, runway pavement, reliability after being shot,... are not the same)

Are you going to fund the upgrade?

Not sure about US military but to some other countries' military, acquiring commercial engines for military use, with a reliable supply of both engines and parts, is hard. E.g. if China and Russia can source modern commercial engines independently and reliably, then then they would very much like to use them on their military transports, or even bombers.

@KorvinStarmast Upgrades of that sort tend to be self-funding...

Some do; the C-17 you mention uses the Pratt & Whitney PW2000 which is also used on the Boeing 757. The USAF and USN also fly the C-40 which is the military variant of the 737 and carries the same engines.
Generally the answer is that military aircraft are built on spec for the military which is a bit different than the way the civilian market works. Civilian builders shop a design around to airlines to get some deposits then build the airframes (the notable exception being the 747 which was largely the idea of Pan-Am CEO Juan Trippe). This often causes there to be new aircraft every few years on the civilian side as Boeing needs to stay in business... On the contrary the military will put out a request for designs to meet their needs, evaluate the submissions and chose what is to be built. They can do this as often or as little as they so please (or as budget allows). If there is no active conflict or need for new tech then the military will keep flying what they have. Many military aircraft have cutting edge tech from the era they were designed in, they may however be dated by todays standards.
Much like the FAA here in the US the various military branches have their own certification programs and regulations thus upgrading and bringing in new gear may require something to be approved this can unfortunately stifle new technology being included due to high time and cost of approval. Similarly military requirements may be different, while a civilian airframe may suffice they may have takeoff length requirements or something similar that necessitate more thrust than their civilian counterpart thus variances in outfitting may occur.

Is it relevant to bring in differing cost pressures? My (perhaps mistaken) understanding is that militaries have much less problems with regular operating budget than extraordinary budgets, such as for upgrading or new acquisitions; whereas commercial airlines are much more sensitive to operating costs, and consequently, commercial airlines are more willing to pay for fleet upgrades more regularly than militaries. Militaries have a harder time justifying new acquisitions if their expected threat/mission profiles haven't changed much, as you pointed out.

Nitpick. Is the 757 "modern"? It first flew nearly 40 years ago and has been out of production for nearly 15.

@DavidRicherby It was reasonably modern when the C-17 was built. The C-17 first flew only 8 years after the 757 entered service.

The 747 was actually based on a design for a military aircraft (it came out of Boeing's failed entry in the contest to design and build the strategic airlifter that ended up being Lockheed's C-5).

Most military transports use engines that were modern when the transport was developed. 30 years later, the engines are outdated, but buying 4 new engines costs in the region of $100 million (and that's not counting the redesign and recertification) so that's rarely, if ever, done.

@DavidRicherby It's the redesign and recertification that makes it cost-prohibitive. This is even worse for a small air force with only 5 planes, as the fuel savings for the 5 frames would never come close to the up-front costs. The only way it would ever make sense for a small air force would be if a larger one had already absorbed the up-front R&D and recertification costs.

@reirab But it turns out that the $100M claim is actually per-plane, as the answer has now been edited.

There are several reasons, although all of them can be reduced to a single one: they have different requirements:

Military aircraft are most of part of their life on idle, in a hangar. We do not want to use military aircraft; we only use them when there is a conflict. That kills any economical trade-off of fuel savings for example.
Mission of military aircraft is extremely different. No discussion about fighters as they are flying at higher Mach number (where commercial airplanes engines are not useful), concerning transport aircraft the commercial one are optimized for fuel saving that creates an expensive engine that is amortized with fuel savings along the life of the airplane and transport military airplane fly very often.
There are requirements from military aircraft not satisfied by commercial engines, like for example, being able to land in sand or bumpy terrain. Engines from military aircraft are protected against that.

Saying that, there are some commonalities that engine manufacturers try to achieve, but that can be found at component level (i.e. having the same turbine for some stages).

"we only use them when there is a conflict" ahem, if you would do that, then the conflict would be a bit one-sided, since your side would not know how to use those aircraft.

nor the other side

Also lower fuel consumption for the same range means more payload (all else being equal, which it never is)

Military planes don't just sit in hangars while there's no war on. They're used for training. A lot.

Can confirm, I live near an air force base, they're out there almost every day.

@DavidRicherby: And for humanitarian missions and general heavy airlift, in the case of military transports (i.e., the ones that start with a C).

Actually, the Russians (used to) work like that, going as far as to design the aircraft for limited nr of running hours (to make them cheaper).

Yeah, military transports definitely don't just sit in a hangar until a conflict. However, it's true that they don't accumulate cycles and time as quickly as their civilian counterparts. Airliners are typically kept in the air as much as reasonably possible, as airliners sitting on the ground generate no revenue.


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How can I reduce the responsivness of my homebrew brake system?
I have a hydraulically actuated aircraft brake system.
Each main landing gear are equipped with brake disk hydraulically operated. The actuation is realized independently for each wheels by means of the correspondent control valve which controls pressure delivery to the brakes. Each brake control valve is connected to each pedal brake. When the pedal brake is depressed, the control valve will open and deliver a variable pressure to the brake adjusted by the pedal angel.
The problem is the Brake is too responsive. When the pedal is depressed slightly, the aircraft suddenly stop.
What is the main problem? Is it the hydraulic flow to the brake disk too high?
Can I install a "restrictor valve" from the brake valve to disk to restrict the flow and make the brake smoother?
if so, how can i determine the size of the restrictor valve?
or the pressure to disk brake is too high?

the function of accumulator is for emergency

What is the make, model and year of the airplane? Is it a standard brake system, or modified? Has this problem suddenly started, or has it always been like this? Do both left and right brakes act the same?

it is a development design. this problem suddenly start when the design is installed and always like this. the left and right act the same

I agree with Frederico, you'll need a valve that controls pressure instead of flow. I am a bit worried about your design in general though, if you loose hydrolic power, you'll loose your brakes too. Do you have backup HPU's and safety systems that can shut down leaking systems so the rest is still working? What else is connected to this system?

the pressure to disk brake is too high?

That is sure, that is the only parameter that can influence how much braking authority you are using.
Given the schematic you posted, my otherwise uninformed opinion (as I don't have pressure measurements, or other data), is that you should investigate your brake valve.
It is probably not providing a sufficient pressure drop even when slightly open. This could be due to the valve model.
Yes, your suggestion to have a restrictor valve (or an O ring inside the pipes) should be a suitable approach, but it depends on the solution you are looking for.
The pressure will drop when the brake fluid is moving, but the equilibrium state will not change, if you keep your pedal slightly depressed your aircraft will still come to a complete stop, simply it will do so slightly later.
If your intention is to have the braking authority controlled by the pedal, what you really want is to change the pressure reaching the brake disk with the pedal.
No static solution is viable in that case: you will need a valve that lets you control the pressure received by the brake plate with the pedal deflection, i.e. you probably have to change your brake valve, or you have to install a system that dynamically adjusts the pressure downstream of the brake valve.

the pedal travel is about 15 degree max, and the plunger is 40 mm.
pressure from hydraulic power is 1500 psi max.
should i change the valve or just modify the mechanical link between pedal to valve?
maybe expand the travel of the pedal?

@RahmatAliAkbar that I cannot answer. It depends on the type of valve, the way the mechanical link works, etc. You will have to decide how exactly to modify your system, either by trial and error, or by having someone with expertise come at your location.


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Was there more than one incident or accident where an Airbus FBW aircraft reverted to mechanical backup?
There was an accident Smartlynx A320 training flights MYX-9001 at Tallinn on Feb 28th 2018, where ELAC pitch control failed due to fault in the stabilizer actuator, and then both SECs failed due to the command and monitor boards responding differently to a short bounce, so only mechanical backup was left for pitch control (fortunately the crew managed to land the aircraft and had just some broken panels).
It is the only instance I heard of where the mechanical backup had to be used. Was there any other incident or accident of an Airbus FBW aircraft (A320 or later model) where only mechanical backup control was available?

Probably yes, because, Airbus is a pretty old manuafacturer. From the A310, to A380, to A350. So yeah, probably yes.
But you can never be sure.

@AirCanada001, the fact that A380 and A350 were certified without mechanical backup suggests otherwise! Yes, none of the aircraft you mention have mechanical backup (the first because it is not a backup, the other two because they don't have any (hydro)mechanical link at all).

I guess that's true, but I feel like that just makes the plane more dangerous. And if just the A320 has mechanical backup, just think of how many planes the A320 family has sold! I think we can agree that if we went digging in the crash history of Airbus, we would be able to find more than one.

@AirCanada001, I am actually certain none of the fatal A320 accidents qualifies. Also, yes, may A320 family planes sold, but they had only 47 hull loss accidents, of those only 15 had fatalities and that includes pilot errors and unlawful interference.

A rapid search on google + avherald provides no results a part from the Tallinn accident: https://www.google.com/search?q=site%3Aavherald.com+%22mechanical+backup%22

Probably No. Considering the Design of Airbus Aircraft, Mechanical Backup is only possible in the earliest implementations of FBW (as in the case of A320) have mechanical backup to prevent complete loss of control. The Newer A380s, A350s (specifically) does not have mechanical backup built-in. The A350s has really high-redundancy built-in to prevent a complete loss if control, which is highly unlikely to happen.
The Accident Investigation Report on Page 90 specifically states:

Considering the remoteness of the loss control of both elevators,
there is no specific crew training for MECHANICAL BACKUP in pitch
during approach, landing and take-off.

This statement provides a hint that such incidents might not have occurred earlier. If such situations were frequent or at-least would have occurred earlier (and investigated) then, it is most likely that crew-training would have been given for using mechanical backup.

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text:
How can a pitot tube freeze when it's heated?
Reading Why turn off pitot tube heating?, it appears that the pitot tube heat can be switched off to extent its lifetime and also in case of short-circuit.

(Thales pitot-static probe, source BEA)
On airliners the probes seem to be heated during the whole flight. This makes me ask myself different but related questions:

Accidents occurred due to probes freezing. How can a heated pitot probe freeze?
Extending the life of the tube seems a questionable choice, I'd rather expect the technology to be improved and be able to sustain permanent heat. Heating a small metal device from -56°C to 5°C (or maybe more, say 100°C, taking into account comments) looks like feasible (not taking into account air friction) ⇢ The problem seems to be how to transfer enough heat from the metal (which is very hot) to the ice accretion.
A short-circuit is easily terminated by a fuse or a circuit breaker. Why does the crew have to worry about switching the heat manually, adding a possibility to have it OFF unintentionally?

I don't know what temperature pitot tubes on a jet are heated to, but it is far far hotter than 5°.  Hot enough to melt your fingerprints off in a fraction of a second (literally...  and I know from first hand experience...  more than once....)

Also, the "how can a heated pitot tube freeze" question is more of a physics question with an answer that would include something about rates of heat transfer and how many joules the heater produces -versus- the temperature and speed of the air/moisture that it comes into contact with.

@Lnafziger: Thanks, corrected. We can heat a large windscreen, it would be interesting to know why it's difficult to heat a small tube. Jets are not short of joules. If there is no answer from the Aviation community, I'll move the question as suggested.

Well, windscreens get ice on them sometimes too!

According to this pdf, a smaller pitot tube submersed in ice water will still reach an internal temperature of 270° C.  I can't imagine how hot they get when at a normal ambient temperature!

With respect to the circuit breaker termination... Interestingly, I was working a 767 not too long ago. It had a "Pitot Heat" message while on the ground with engines off. Turns out, the pitot probe was internally shorted, causing it to be full hot all the time, and no breaker tripped. The probe was probably designed to fail in this way, but my co-worker who inadvertently touched the probe didn't think it was such a brilliant design. Also, not all aircraft have a switch. Some do, and some don't. I think more of the modern aircraft have built in logic. I'll update the other thread.

@mins: The probe element, which seeks a ground, shorted to the probe, internally, and "electrically after" the heating element. Again, I believe the probe was probably designed to fail this way as a short on the "front" side of the element would pop a breaker. The current draw was still within the normal parameters of the circuit breaker, but the aircraft knew that pitot heat was on while on the ground with engines off - hence the status message. My point was that just because the probe is shorted, doesn't necessarily mean it'll pop a breaker. My coworker found that the hard way.

Captain Bill Palmer, in his book "Understanding Air France 447" has a section dedicated to answering that very question as it pertains to AF447. Although there is no way to know for certain he puts forward some possibilities.
He quotes a commenter on a website:

One commenter on the Weather Graphics website’s AF447 article provided this interesting observation: “I'm an aircraft icing specialist and wanted to point out a factor that hasn't been discussed much … high ice crystal concentrations. I've seen flight test data from power rollbacks due to flight in high ice crystal environments … In our case, the crystals collected within heated, aspirated Ram Air Temperature sensors, forming a 0 ° C slush…”

He notes that just before the pilot tubes clogged, the sound of ice crystals hitting the windshield could be heard on the CVR.

Ice crystals bounce off the exterior of an airplane and cause no visible ice accretion, but they can enter the probe inlets. When highly specific climatic conditions exist in combination with certain combinations of altitude, temperature, and Mach, the concentration of ice crystals entering a probe can exceed its capacity to melt and evacuate the moisture through its drain holes. The result is that the ice crystals form a physical barrier within the probe that disrupts the measurement of total pressure.

The particular type of ice that may have been responsible was a substance called graupel.

Graupel forms when tiny supercooled water droplets adhere to snow crystals to the point that they engulf the snow crystal itself.

Graupel. Photo from Wikimedia commons
Capt. Palmer notes factors that make graupel a possible suspect:

No airframe icing. The supercooled water theory is discounted by the fact that the A330's icing detectors were not triggered.
Graupel has large enough particles to be audible on the voice recorder. It takes a particle with enough mass and inertia (a given density) to hit the fuselage with a sound, instead of flowing around it with the relative wind, like snow.
Graupel has enough mass to temporarily overwhelm pitot anti-icing when concentrations are high enough. The pitot tubes are hot. But even if you put a snowball on a hot skillet it does not melt instantaneously. If there is enough mass in the blockage, and in combination with new particles being added to the blockage as the first ones melt, it may exceed the pitot tubes capability to melt the obstruction as fast as it is introduced. Graupel is of significantly higher density than snow.
Graupel has sufficient blocking properties to prevent efficient transmission of dynamic pressure within the pitot tube.For example, water can flow and transmit pressure within the pitot tube, though it too can alter pitot-static readings, a physical non-fluid blockage could shield the pressure sensing port.
The likely presence of snow or similar form, as evidenced by the St. Elmo's fire discussed by the crew. The accident report stated that the sound of ice crystals hitting the aircraft can be heard about 20 seconds before the airspeed loss and autopilot disconnect.

It must be noted that the exact cause of icing problems on the A330 was never completely identified but it was specific to the particular brand of pitot tubes originally installed. Airbus was in the process of replacing them all with pilot tubes from a different manufacturer.

So a possibility could be that the sudden arrival of the a large quantity of GS ice cannot be melt by the heat. Thanks for having named it. This calls indeed for another question: What would be the cost of improving probes to get rid of stubborn ice when heat is not adequate, rather than to stop providing measures for an undetermined amount of time. I'm suggesting a simple solution: Mount two opposite probes on a plate (active and backup) and rotate it when the active one stops working. It surely can't be a good solution, but other solutions must exist.

I don't know what the design differences are but Thales, the company that made the pitot tubes redesigned them and the newer model had fewer icing problems. They also had previous problems with BF Goodrich pitots and water ingestion. BFG redesigned these too. It is not completely avoidable but I don't think it is really a huge problem. The other times it happened it was transient and the pilots simply hand flew for a minute until it cleared. On AF447 it only lasted about 30 seconds. Just being aware that it can happen and knowing the correct reaction is the key.

To my knowledge graupel was discounted in relation to AF447 a long time ago, it's too large for that. In the majority of cases graupel can also be detected by radar (assuming the crew were using it correctly). Ice crystal icing is a different beast, however.

Probably not relevant to airliners, but I had a pitot icing incident on my Lancair that was interesting. The pitot heat was functioning correctly throughout. I had flown through a lot of rain early in the flight, and some liquid water had entered the pitot and gone past the heated portion of the probe and deeper into the lines connecting it to the ADAHRS. Later in the flight I climbed into colder air below 0 C. All was still well until I started my descent and pitched forward. This pitch angle caused the liquid water to run into a different, colder portion of the line and freeze, blocking it.

To answer your questions in order:
1) Pitot tubes are certified to withstand icing under particular circumstances: Within a given temperature range, precipitation amount, altitude etc. If they are operated outside of those ranges then the heating systems may not be effective. In the case of AF447 it was also important that they experienced ice crystal icing and not supercooled water icing - the two respond to pitot heating differently and the same certification requirements can't be used for both.
2) Automated systems are not, yet, perfect at detecting icing conditions. You don't want a system where the pitot is always on, with no possibility to turn it off, for safety reasons and you don't want an automatic system because it might fail to detect icing conditions and hence not activate the heat. That said, in my experience it's very rare to have the pitot heat off: There's not really much point. The crew has to have the discipline to turn it on at the beginning of the flight but after that an automatic system is not helpful if the heat is supposed to remain on anyway.

According to the book I quoted in my answer, on the A 330 pilot heat is on anytime the engines are running. There's no switch

TomMcW - they can be turned off, however - anything electrical on an aircraft has a circuit breaker

"You don't want a system where the pitot is always on, with no possibility to turn it off, for safety reasons": I covered this point in the question (last bullet). A circuit breaker is necessary.

"Pitot tubes are certified to withstand icing under particular circumstances": The question would be: Is the certification standard adequate? I understand that if this was easy, it would be done, but I don't understand clearly the difficulty.

@mins The certification standard is sometimes updated. This was done after AF447, for example, to better cover ice crystal icing conditions.


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Where do airports use 3-bar VASI for the visual glideslope?
What are some airports that have a 3-bar VASI system?  I am trying to find some locations to compare what the chart supplements say to the supplements for those with 2-bar VASI systems.

Runway 8 at Albuquerque International Sunport Airport (KABQ) has a 3-bar VASI.
KABQ's current Chart Supplement page1 lists the VASI for Runway 8 as a VASI(V6L): a 3 bar, 6 box VASI located on the left side of the runway. The airport diagram also depicts the VASI as a V3: a three-bar VASI.

The VASI bars are also visible in aerial images, such as here on Google Maps:

1The current Chart Supplement page will expire and this link will be broken. For future reference, the updated Chart Supplement page can be found elsewhere, such as on this SkyVector page.


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How do you determine whether you can us LNAV/VNAV minima on an RNAV approach?
If we look at this approach plate it has

LPV DA
LNAV / VNAV DA
LNAV MDA
CIRCLING

I understand that if you have WAAS you can shoot the approach to LPV DA minimums. If you have only a GPS with a DME providing lateral navigation you can shoot the LNAV MDA. If you are more than 30 degrees off centerline you shoot the circling. So my question is, how can you shoot the LNAV / VNAV DA on a non-precision GPS approach? Does this require a special GPS that has vertical guidance?

Possible duplicate of What is the difference between LNAV/VNAV and LPV minimums on an RNAV approach?

The STC documentation provided with the GPS / FMS installation will indicate the type of minima it can go down to.
Typically, GA aircraft like a Garmin 430/530 will only be certified down to LNAV minima.
Business type aircraft with FMS's may be certified to LNAV/VNAV minima.  These installations use a barometric altitude input to calculate a pseudo glidepath to be displayed.

I would like to add that you can turn waas off in a garmin 430 and that's another way you could know.  The other way is fly the approach in vfr and if it says LPV on the GPS then you have it.  If your renting ask the people you are renting from. I can only assume there's a higher cost for updates(or miantance I guess) with WAAS so find out who pays the bills.

This answer is misleading, many 430/530 units can do LPV, you just need WAAS.


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Which should I get a FAA glider licence or a Canadian glider licence?
I plan to operate in the Caribbean (Antigua, under ECCAA jurisdiction, which does not have a glider rating of its own) and not in the USA or Canada. I am looking at which one would be require less work and time on my side. I plan to give rides in my country and practice the sport.

The Caribbean includes multiple jurisdictions/countries that may have their own aviation regulations on certificates they accept from out of country. Can you specify (country/jurisdiction) where you intend on operating.

The problem with my country (antigua and barbuda ) ECCAA is that they do not have any glider exams or glider clubs or schools.

To the suggestion to close as opinion based: while the title suggests searching for an opinion, the question specifies clear objective criteria of “less work & time.” This isn’t seeking subjective opinions.

This is heavily dependent on the local jurisdictions you plan to operate in and what their laws are.
First off you must find out if your desired countries of operation accept foreign certificates. This varies heavily all over the world and can range from full no questions asked acceptance, to you needing to simply take the test again (in that country) through any various case you can think of.
Second you need to find out what certificate you need. Here in the US to give rides (and receive compensation for such) you need a commercial certificate. This looks like it extends to gliders as well.
Hours.
The FAA requires a few more hours than the Canadian certificate will,
FAA

Are at least 16 years of age; and
Have logged at least 10 hours of
  flight time in a glider and that flight time must include at least 20
  total glider flights, and
Have 2 hours of solo flight time in a
  glider, and
Have passed the FAA written examination; and
Have passed the flight exam with a FAA Examiner.

Canada

A minimum of 6 hours of flight training under the direction and supervision of an instructor
At least 2 hours of solo flight time, including a minimum of 20 takeoffs and 20 landings

Right off the bad Canada requires 4 less hours which, no matter how you spin it will be cheaper (since you have to pay for less time).
Here is the US if you are not a citizen you will need to pass an NTSB background check to train. I do not know if Canada has a similar requirement.
Travel, assuming you are in the Caribbean already it may be cheaper to travel to Florida (or the like) to train then go all the way up to Canada for your training.
Edit:
According to this document the ECCAA does issue glider ratings

2.1.2.3 RATINGS ISSUED
(a) The Authority may issue the following ratings for pilots
  (i) Category ratings in the following aircraft:

(a) Aeroplane;
(b) Rotorcraft;
(c) Glider;
(d) Lighter-than-air;
(e) Power lift.

The problem with the canada one is that the glider license written exam is not public, in terms of questions, while in the usa the questions are public most of them. In the states it is 14 not 16 and they do not require a TSA clearance, for glider.

They might do but it does not make sense since there is not glider schools in the country but there is a pilot school for aircraft.

The difference in hours required only matters if you can complete the training within those hours.  If you need a few more hours to learn the material, then the legal minimums will become irrelevant.

Very true, but there are those that complete in the minimum time so I felt it appropriate to mention. For the record my PPL took well over the 40 required hours.


text:
What is the structural significance of 'dimples' on the fuselage of a Boeing 747?
I recently watched the following video:

In the video there is a mention that there are 'dimples' visible on the fuselage of a Boeing 747, when it is on the ground. It then goes on to explain that once the fuselage is pressurised - the expansion helps to "smooth" out the dimples and it will be flat.
I am curious as to what the structural significance is for 'dimples' on the aircraft?

Related: why-does-the-757-fuselage-bend-more-on-turbulence-than-those-of-other-airplanes

That's just oil canning of the unsupported areas of skin between stringers and formers, and when pressurized the skin stretches enough to remove them (18:00 in the vid).  The fuselage diameter will swell a little bit, maybe 1/8 or 1/4 inch, when pressurized.

Would I be right to assume that these "dimples" are, therefore, found on every semi-monocoque aircraft?

Only the pressurized airplanes.  No such dimples on unpressurized  Cessnas for example.

No not necessarily.  Sometimes you see oil canning, sometimes you don't.  It's more prevalent on really big airplanes where the skin, in relation to the overall size of the structure, is thin you might say.


text:
What is the meaning of R88/70D in this METAR from Ashgabat International airport?
The following METAR is from Ashgabat airport (UTAA)

UTAA 071300Z 13006KT 9999 FEW050CB BKN050 BKN100 15/06 Q1013 R88/70D
  NOSIG

What does R88/70D mean, I couldn't find any references?

I assume it was a typo, as R88/70D is not a correct METAR format. According to this website with historical METARs the METAR of today at 1300Z at UTAA was:

METAR UTAA 071300Z 13006KT 9999 FEW050CB BKN050 BKN100 15/06
             Q1013 R88/CLRD70 NOSIG=

All other METARs from UTAA today contain "R88/CLRD70 " as well.
R88/CLRD70 means: all runways are cleared (no more deposits), and a friction coefficient of 0.70.

My guess: R88: all runways, 70: friction coefficient .70, D: dry.


text:
In which accident a helicopter and plane collided after a landing gear failure?
Many years ago (35+ years), my father told me a story regarding a VIP that was on a small plane that had landing gear failure. It was decided that instead of attempting a landing, a helicopter would be used to attempt an air to air rescue. The rescue failed with both aircraft crashing. Does this sound familiar to anyone? I would like to know the story behind it if I can find it. I believe the crash would have occurred in the United States in the 60s or 70s.

On its face, that sounds ridiculous.   Airplanes with gear-failures rather commonly do belly landings.  Its not risk free, but its far better to be on the ground, sliding down the runway, than trying to switch aircraft in midair.

+1.  Air to air "rescue" using a helicopter?!  I have never even heard of the military trying such a thing, which would be fraught with peril even if practiced regularly.  To try something like this with untrained, unbriefed civilian pilots just to avoid a belly landing seems ludicrous.

You are both correct, I misremembered the specifics of the story.

Unbriefed dis-similar formation flying (by possibly untrained pilots) is almost as bad.  I wouldn’t let a helicopter get anywhere near me personally.  A very preventable tragedy.

I was able to get the details after speaking with my father:
This was the Merion air disaster where a helicopter attempted to ascertain the cause of a landing-gear malfunction and collided with the airplane. It was not a rescue attempt as I originally thought.


text:
How can I estimate pressure altitude?
How do I find pressure altitude?
Find pressure altitude using rule of thumb for 1498 feet when the altimeter setting is 27.83" Hg.
I did (29.92-27.83)*1000+1498=3588
Did I do this correctly?

You are 1498ft above the place where the pressure is 27.83InHg. So how high are you above the place where the pressure is 29.92InHg?
27.83 is 2.09InHg higher than 29.92, ie roughly 2090ft higher. So you are 1498 + 2090 above the place where the pressure is 29.92InHg, ie your Pressure Altitude is ~3588ft.

This calculator is coming up with 3488 ft
http://imageserver.fltplan.com/PressureAndDensityAltitudeCalc.htm?USER=PILOT
But your formula looks correct to me and you did the math correctly.
Not sure why the 100 ft difference.

The 100ft difference is due to the fact that "(29.92 - QNH) * 1000 + h" is just an approximation. The website uses the exact equation to compute the pressure altitude.


text:
What is meant by "Outbound leg timing begins over/abeam the fix, whichever occurs later" in FAR/AIM 5-3-8?
In FAR/AIM, 5-3-8. Holding part, There is a sentence that says

(b) Outbound leg timing begins over/abeam
  the fix, whichever occurs later.

I got to know that the word 'over' is for parallel or teardrop entry. But I still can't understand the intention of 'whichever occurs later'.
Could anybody explain this more specifically?

"Over" would be appropriate to disambiguate what happens in parallel or teardrop entry.  But I don't understand the "whichever occurs later" logic.  The sentence makes most sense to me with the final word removed.

BowlofRed/ Thanks, now I realize the meaning of 'over'. Still the last sentence is obscure, so I modified my post a bit.

The text is written that way to take into account the various type of holding entries. In case of a parallel or teardrop entry, the outbound leg starts after passing over the fix. In all other cases the outbound leg start after passing abeam the fix, following a turn that starts over the fix.
Case 1: Established in a holding pattern
So when established in a holding pattern, the outbound leg starts abeam the fix.
The sequence is:

inbound leg
pass over the fix
turn outbound
pass abeam the fix
outbound leg
turn inbound
repeat from 1.

In this case it is clear that the time of the outbound leg should start when you pass abeam the fix, which occurs later in the sequence.
Case 2: Entry into holding pattern

Case 2.1: Parallel Entry into holding pattern
When entering the holding using a parallel entry ((a) in the diagram) the sequence  is:

fly to the fix
pass over the fix
turn outbound course
outbound leg (on non-holding side)
turn to inbound leg
intercept inbound leg
follow sequence for established in a holding pattern

In this case the timing of the outbound leg should start when you pass over the fix. From this, it follows that the outbound time will include the time spent in the outbound turn (3.).
Case 2.2: Teardrop Entry into holding pattern
When entering the holding using a teardrop entry ((b) in the diagram) the sequence  is:

fly to the fix
pass over the fix
turn outbound course
outbound leg (30 degree into holding side)
turn to inbound leg
intercept inbound leg
follow sequence for established in a holding pattern

In this case the timing of the outbound leg should start when you pass over the fix. From this, it follows that the outbound time will include the time spent in the outbound turn (3.).
Case 2.3: Direct Entry into holding pattern from holding side
When entering the holding using a direct entry from the holding side ((c) in the diagram, sector on the holding side) the sequence  is:

fly to the fix
pass over the fix
turn outbound
pass abeam the fix
outbound leg
turn inbound
follow sequence for established in a holding pattern

In this case it is clear that the time of the outbound leg should start when you pass abeam the fix, which is later in the sequence.
Case 2.4: Direct Entry into holding pattern from non-holding side
When entering the holding using a direct entry from the non-holding side ((c) in the diagram, sector on the non-holding side), you may not complete the turn before being abeam the fix. In that case the sequence is:

fly to the fix
pass over the fix
turn outbound course
outbound leg
turn inbound
follow sequence for established in a holding pattern

In this case it is clear that the time of the outbound leg should start when you pass over the fix. From this, it follows that the outbound time will include the time spent in the outbound turn (3.).

In a 2018 publication, "A Treatise on the Holding Pattern:Expelling the Myths and Misconceptions of Timing and Wind Correction", the complete mathematical solution of the generalized holding pattern problem was finally solved.
The results are completely analytic and are valid for any wind direction and wind speed up to 99.99% of the aircraft true airspeed. The results show that the outbound time should start when the aircraft has crossed the fix and turned to the outbound heading.
The analysis is valid for any constant rate of turn (standard, bank-limited, or specified). The solution provides the inbound wind correction angle, outbound heading and outbound time, which allows the aircraft to intercept the inbound course exactly at the point that satisfies the required inbound time or inbound distance (i.e. ATD) from the fix. Thus, it is no longer necessary to locate the abeam point.
In the AIM (5-3-8), for cases where the abeam point cannot be determined, the recommendation is to start the outbound time when the outbound heading is reached.
When the windspeed ratio (wind speed/TAS) is greater than 1/3 with a quartering headwind, the shape of the track of the aircraft in the holding pattern is such that it is impossible to determine the abeam point. However, there is another property of the holding pattern solution that shows that if the outbound time is started  at the point the aircraft has turned to the correct outbound heading, the outbound time is the same ,for a given relative wind angle measure from the inbound course, whether the aircraft is flying left (non-standard) or right(standard) holding patterns.
If the time is started at the abeam point, the outbound times will be different when flying standard or non-standing holding patterns. The fact that abeam point does not need to be determined, reduces pilot workload during the hold.

It's nothing to do with the type of entry, it's down to your accuracy of flying.
If you are flying accurately, you will pass directly overhead the holding fix, in which case you hit the stopwatch as you pass overhead. But if you fly slightly to the side, for whatever reason, then you hit the stopwatch as you pass abeam the fix as being a rough approximation of the overhead.

How could you pass both over and abeam the fix (so requiring the "whichever occurs later" wording)?


text:
Does diving after a take-off help gaining altitude?
I have often read fictions about aircraft, where a pilot does an action that I cannot explain:
During a takeoff with an heavy aircraft (four motors for example), the pilot rolls to the end of the airstrip, and starts to climb.
Then he says: I am too heavy to climb enough in order to avoid the mountain/trees/whatever obstacle in front of us.
So the pilot starts to dive to the ground in order to gain more speed, and then he climbs again and is able to have enough altitude.
How do you explain this action?
Considering the drag, why does the dive gain enough energy to go to an altitude above the one reach by the take off?
I might not be clear, please don't hesitate to ask details.
Here is a schema:
    Not enough         /Climb enough
        /  \          /
strip  /    \        /
              -------

I don´t think you are using the word glide for what it is usually understood to mean: fly without power exchanging gravitational potential energy to maintain airspeed. Maybe you mean flying in ground effect to accelerate to a safer speed before maneuvering?

Hi I am not a native English speaker. I mean by gliding: flying with a negative AoA, the nose of the airplane pointing to the ground, with motors powered on. Thus the airplane is exchanging gravitational potential energy to increase his airspeed

@totalMongot  What you describe is diving, not gliding.  Gliding is a power off maneuver.

@Skip Miller Thank you for the clarification, and sorry for the mistake

Flying with a negative angle-of-attack near the ground will definitely lead to disaster.  It never fails.  Unless the aircraft is inverted.

You may have possibly meant to say a nose-down pitch attitude.

Did you really mean your diagram to show the plane diving to an altitude below the landing strip?  Not generally recommended, though I have done it.  Stead airport in Nevada, where the ground east of the runway drops a couple of hundred feet to a usually dry lake bed, and an overweight flight instructor in a tired C-150 on a warm day.  Not really a glide, though: more like a shallow dive at full power :-)

When an aircraft can barely climb after take-off, it may be flying on what is called 'the backside' of the power curve.
Flying at very low speed:

costs a lot of power because of high induced drag
means that the engines are inefficient because they are optimised for higher speeds.

As a result, the excess power available, that is the difference between the required power and the maximum available power, is very low when the aircraft flies close to the minimum flight speed. And the excess power is what is needed to climb the aircraft.

When the aircraft is flying below the speed at which the best angle of climb is achieved (Vx), it will be able to improve its climb angle by accelerating. To do so, the aircraft needs to use available power to accelerate, instead of using the power to climb.
Stopping the climb or even descending a bit will convert the available excess power and optionally height (potential energy) into speed. While this initially does not give extra clearance above the obstacle, the available excess power increases drastically. This in turn gives the ability to climb at a much steeper angle, allowing the aircraft to clear the obstacle.

Excellent answer!

Bear in mind that fiction often (usually?) takes liberties with the truth of a technical situation. That said, let's say your 4-engine aircraft is a Boeing 747-200 with JT9D-7Q engines (because that's what I still have a QRH for).
And let's say the paperwork says you weigh 620,000 lbs—it's an empty freighter you're ferrying from Santiago, Chile to Buenos Aires. You look in the performance tables and come up with the following:

V1 is 130 knots
VR is 140 knots
V2 is 156 knots
target rotation attitude is 16° nose up

Unbeknownst to you, the ground handling company decided to pick up a little money on the side and put 180,000 lbs of cargo on board for an equally corrupt operation in B.A.
So, you really weigh 800,000 lbs, the numbers for which are:

V1 is 160 knots
VR is 173 knots
V2 is 183 knots
target rotation attitude is 13° nose up

You stagger off the ground—God help you if you get a bad gust—with your reference speed 27 knots slower than it should be and your nose 3° higher than it should be. My guess is that you would be on the backside of the power curve, but whatever, your performance is going to be less than it should be.
Some miles ahead you have one of the highest MEAs in the world, 24,000 feet as I remember. Mt. Aconcagua at 22,841 feet (highest peak in the Andes) will be just off to your left. You often have difficulties getting that high that soon. You wouldn't make it today.
The solution: lower the nose and speed up.
And by the way, you're probably going to have to land short of B.A. for fuel. Personally, I'd go to Mendoza, Argentina.

I don't understand. You lower the node and trade potential energy for kinetic. Then you need to raise your nose again and ... Convert all your gains back to potential. Without counting drag, this sounds like a 0 sum operation

@Antzi No, the goal is not to trade potential energy for kinetic. The goal is to increase your speed to that which will enable the wing to perform better. Now, if you're on the backside of the power curve and are already at max power, the only way you'll be able to increase your speed is to sacrifice some altitude. Then, when your speed is up to the right speed you'll be on the front side of the power curve and have performance capability you didn't have at the same power setting on the back size. I suggest doing a search on "back side of the power curve."

I'm hoping the sentence Unbeknownst to you, the ground handling company decided to pick up a little money on the side and put 180,000 lbs of cargo on board for an equally corrupt operation in B.A. isn't from bitter experience :|

@Jamiec Well, it's from experience but never that turned bitter and never anywhere near 180,000 lbs. Back in the 1990s in freight runs out of B.A. and Santiago, some overloading was to be expected for whatever reason. The two worst overloads I experienced, though, were out of Miami and Chennai (then called Madras). The company did some research on the Miami to Trieste incident because it caused an unplanned fuel stop in Paris. We were 30,000 lbs over due to cargo that had been loaded in the lower holds but not shown on the paperwork. Madras was also about 30,000 lbs but wasn't intentional.

@Antzi don't forget you're pouring 100% power in the whole time.  Getting the speed right to climb is what you are after.

@Antzi if the wings created lift, and the engines produced power, in a way which was completely linear with airspeed, then yes it would be a zero-sum game. But wings are optimised for certain airspeeds (for an airliner, usually higher speeds), and turbofan engines can produce more thrust at lower altitudes (more air to push) and higher speeds. Similarly if you fly faster you can retract flaps/slats and have less drag on the airframe. As such, it's not a zero sum game - by flying lower and faster you may be able to put more energy into the airframe in the same time&with the same amount of power

Looks forward to getting to the "overloaded plane" chapter of @Terry's blog

The Pilot's Operating Handbook (POH), which is specific to an individual airplane, lists two speeds of interest:  Vx and Vy.  Vx is the obstacle clearance speed, and Vy is the maximum rate of climb.  Vx is less than Vy.
Flying at Vy, the plane will climb more quickly (e.g. how long will it take to reach say 1000 feet above the airport) but because you are moving faster over the ground at Vy, you still might hit that mountain because you get to it sooner.
Flying at Vx sacrifices airspeed for altitude.  At Vx you are flying more slowly and are climbing as fast as the plane can.  It maximizes your vertical speed, not your horizontal speed.
As altitude increases, Vx and Vy converge and when they do, you are at the absolute altitude limit for your plane.
In your example, it sounds like the plane took off at Vy, noticed the lack of sufficient climb performance, leveled off or descended to gain speed, and continued the climb at Vx.
I have omitted a discussion of ground effect flying as it would be highly unusual for your four engine large airplane to remain in ground effect for long.

Perhaps I'm misinterpreting what you're saying. If so I'll remove this comment, but consider rewording your third paragraph. " At Vx you are flying more slowly and are climbing as fast as the plane can." But you said in para 1 that Vy is the maximum rate of climb (and I agree), so how can both statements be true. "It maximizes your vertical speed, not your horizontal speed." Not really, it maximizes the altitude gained for the amount of horizontal distance covered. P.S. How old is "older than dirt" (from your profile)? I'm about to turn 80.

The above answer sounds like it is suggesting that Vx is faster than Vy which is never true -- "it sounds like the plane took off at Vy, noticed the lack of sufficient climb performance, leveled off or descended to gain speed, and continued the climb at Vx."

The only time it will work is if you are below Vx, and you do not need to dive to pick up speed under power, reducing pitch angle to level should be enough.  Actually did this once with a model that was too rich (prop RPM slower) and had gained considerable weight from numerous repairs.
Essentially, you climb in stepwise fashion. If airspeed bleeds off below Vx, reduce pitch and
keep climbing.  But doing a rotation at proper speed and climbing at Vx is the best chance of clearing an obstacle.
What you have depicted is more like a zoom maneuver, which might help insure clearing one row of trees if you are slower than Vx, but a mountain 10 miles distant needs Vx right after liftoff.

Thank you. The examples I read off in fiction are in fact about clearing one row of trees a few hundreds meters ahead of an air strip with an heavy airplane

@totalMongot a little fast is far better, then pitch to Vx speed. If you do not see trees and your airspeed holds, you got it. If trees or terrain are still directly ahead, time for plan B.


text:
Are the communications between captain and flight attendants standardized?
Premises

For usual communications between pilots and ATC, a specific phraseology is followed.
In case of an an unexpected event (e.g. a sick passenger), flight attendants and pilots can communicate through intercom.
Pilots (particularly the captain) can speak to all people in the cabin (including flight attendants) through the public address system.

Questions

Do the communications made between the cockpit and the cabin (thanks to the public address system) follow a specific phraseology to deliver information to flight attendants?
Are there some messages following a specific phraseology that trigger a reaction among the flight attendants (e.g. preparation for flying across turbulence), but passenger may think the message is address to them?

I think of the coordination of the preparation of the cabin for the different flight phases (taxiing, taking off,...) or indication of the strength of turbulence (implicating the flight attendant may not begin to move carts along the cabin).

It it worth pointing out that radio phraseology needs to be standardized because each pilot talks to many different ATC facilities and each ATC controller talks to pilots from many different carriers. So everyone needs to speak the same language, unless some participants in the system learn several different languages. On the other hand, local communication between pilots and cabin crew can be left to internal company procedures without the same kind of problems.

Been waiting for an answer but none coming so - guesswork and experience, since no citations or direct knowledge.
It's a mixture of both.  Often, cockpit to cabin communication is one to one.  Rather than use the cabin address, the crew will call a specific station for example, the rear galley.  So if the captain wants a coffee, they will not use the cabin address, nor is there any need for a formalised language.
Please may I have a cup of coffee?

Other comms may be most effective using cabin address but still not needing a formalised language, for example.
Cabin crew, please take your seats.

This call would only happen after the passengers are belted in, since you are already in turbulence and the cabin crew don't need a formal instruction to buckle up.  In my experience, the initial call to warn of turbulence ahead is made one to one to a specific station, usually the purser or senior cabin crew member.  That person will then instruct the rest of the crew. The fact that the crew has been asked to sit, means that the carts will be stowed and the cabin prepared.  It's just a part of their routine.  In the case of unexpected heavy or severe turbulence, the crew probably do not need a call, since they know about it at the same moment the cockpit crew know but, a specific instruction might be given to indicate urgency.
Cabin crew, please take your seats immediately.

Some comms are most effective with an address and a formal command, for example.
Cabin crew, doors to automatic and cross-check.

This is a safety critical procedure and is therefore specifically addressed ("cabin crew") and a precise instruction ("doors to automatic", "cross check").  It was doors to automatic, not manual, and check the opposite door to make sure the person responsible for that door has done it, and done it correctly.  Note that this particular command is normally given by the purser or senior member, and not from the flight deck.
There is also a call to "all stations" which will call all the station phones and whichever crew member picks up will deal with the comms.
As far as I know, the precise wording of instructions is not regulated but is part of company SOPs and check lists.

Sorry, edited.  SLF, self loading freight = passengers.  1-2-1, one to one.

Nice answer. For the definition of crosscheck, please see this.

Again, since there has been a sparsity of answers, I'll try to add to Simon's excellent answer and give a bit of a different perspective. My answer is dated in that it comes from flying 747-100 and -200 aircraft in the 1990s at the last airline I worked for. Given what I am sure is a wide variability of cockpit crew & cabin crew communication practices around the world, it may still be relevant. Remember, though, this is pre 9/11.
The cabin crew typically would arrive at the airplane before the cockpit crew. The first interaction other than a quick hello as we came onto the airplane was usually the upper deck flight attendant coming into the cockpit within a few minutes of the cockpit crew (captain, first officer, flight engineer) getting settled. Company policy was that the upper deck flight attendant was to check with the cockpit at least every 20 minutes to see if they wanted anything. It's the captain's airplane, though, and she/he could set the tone. I always declined anything until we had reached cruise. Additionally, I would tell the flight attendant that checking every 45 minutes to an hour would be sufficient but that if they just wanted to come up to chat at any time that would be fine. We were usually flying 8 to 12 hour legs. I would also tell them that I preferred to be called Terry rather than Captain, though more often than not they still called me captain.
Company policy was that the purser (chief flight attendant if you like) was to personally come to the cockpit to inform the captain that "all doors are closed, all passengers seated." That was my cue to call for the before-start checklist. Likely the purser had already been to the cockpit earlier to let me know how the loading was going, who was in back, and any problems. I in turn would give the purser the expected flight conditions, estimated time en route and such. I wasn't big on the captain making announcements to the cabin. My policy was to give the info to the purser and let them handle cabin announcements as much as possible.
The next company-required communication was hitting the button that sounds the beep throughout the cabin when we climbed through 10,000 feet, and I'd turn off the seat belt sign then as well. If there were no weather/turbulence problems en route, the next usual communication was a call to the purser shortly before the start of descent. However, typically the purser would have come to the cockpit every couple of hours during the flight to chat.
Descending through 10,000 feet I'd hit the cabin tone button twice and turn the seat belt sign on.
Last cabin communication was hitting the cabin tone button and turning off the seat belt sign after the parking brake was set.
Hajj flights were a special case. The purser was always one of our people, but the flight attendants were supplied by the national airline we were doing the flights for under contract. The requirements included that the captain be notified if anyone became seriously ill. All Hajj flights were required to have at least one doctor onboard, who would be a Hajji as well. The purser would come into the cockpit to tell the captain, and the captain would ask if the doctor wanted to land for a medical emergency (they never did). The captain was also to be notified if someone died. This was not unusual on Hajj flights, and we carried body bags for that contingency. A death was not a cause for landing short of the destination.
There is an area that starts before descent that has religious significance to Muslims because of the proximity to Mecca. It was marked on the IFR en route maps. We were supposed to announce entering that area. I always did that personally because I had learned how to properly pronounce it's name (well, as close as I could). The irony of the situation was that here was a 747 from a Jewish-owned airline, captained by an atheist, telling a plane load of Muslims they were approaching Mecca, Islam's holiest city.

Hi @Terry. Why were deaths common on Hajj flights?

@MarkyMark The typical Hajj passenger for the Indonesians and the Indians, which were the two nationalities I flew the Hajj for, are old and poor. They and their families save to try to get them to Mecca towards the end of their life. The great majority of them have never been in an airplane in their entire lives, so it's a stressful situation for them. There is also the belief, or at least so we were told, that if a Hajji dies making the Hajj, it's a ticket straight to heaven. Also, these were people who hadn't had good medical care through their lives. Lots of toothless people.

I surmised as much, but thanks for the answer.


text:
Are there any Boeing 747 still flying for commercial use?
No American airline flies it anymore, but the Jumbo has been mythic for decades:

ANA B747-400. Wikimedia, photo by Kentaro Iemoto
Is it still possible for a passenger to board a Jumbo Jet?
Which airlines are still operating the B747 in 2018?

FWIW the A380 (and other wide body airliners) is also a "Jumbo Jet" the 747 just happens to be the original Jumbo Jet

Does commercial use == passenger use? There's also the many 747's in use as freighters, are those worth mentioning?

Come over to LHR. There's still loads of them.

https://en.wikipedia.org/wiki/List_of_Boeing_747_operators

@Dave A lot of people consider the phrase "Jumbo Jet" to refer specifically to the 747. I certainly disagree with your suggestion that it can refer to any wide-body at all. Nobody used that term for the DC-10 or the Tristar, so it would be strange to use it for, e.g., the 777.

Why do you have an interest with this place?

I actually just flew home in one last week, on Lufthansa!

@Dave: I thought A380 was a Superjumbo Jet?

It seems we have a Potato Potato scenario here... Then again its largely a term used by non av-geeks so usage is subjective and often not well informed. Most airplane nerds refer to it by its model designation.

@Dave I'm pretty sure most non-specialists also consider the phrase "Jumbo Jet" to mean either "747" or "747 or A380". I can't imagine anyone describing a random wide-bodied plane such as a 767 as a Jumbo, for example.

There are still lots of 747's in scheduled passenger service and at least a few dozen of them will almost certainly remain so for the next 20+ years.
747-400

British Airways has 36 of them with retirement scheduled for 2024.
Virgin Atlantic has 8 of them with retirement beginning in 2019.
KLM has 14 of them
Qantas has 10 of them
China Airlines still has some
El Al still flies them, but is planning retirement in 2019.
Several others around the world

There were deliveries of passenger 747-400s all the way up through 2005, so the newest ones are only about 12-13 years old. The U.S. airlines, however, were among the first customers and had some of the oldest ones. In Delta's case, they literally had the oldest one, as Northwest (which Delta acquired several years ago) was the launch customer of the 747-400. So, while Delta and United's 747s were mostly over 20 years old (some over 25,) many other customers operate much newer ones.
747-8I
While the 747-400s are on their way out, the 747-8Is are mostly only a few years old and should still be flying for decades. These are currently flown by 3 airlines in scheduled passenger service, as well as several others in charter and/or VIP service.

Lufthansa has 19 of them
Korean Air has 10 of them
Air China has 7 of them

While the Delta 747-400s with their lovely 14-seat 1-1 business-class configuration upstairs are unfortunately no more, if you're looking to ride upstairs on a 747, my personal recommendation would be Korean Air's 747-8s.
Other Commercial Operations
There are lots of 747s in cargo service and this doesn't appear likely to change any time soon. The 747-8F is still in production and has accounted for almost all of the recent new 747 orders. It appears that it will remain in production for at least the next few years and possibly quite a bit longer than that. UPS ordered 14 of them a little over a year ago, so that will keep the line going for at least a couple more years by itself.
Aside from the numerous 747-400 cargo and charter operators, the following operators all fly the 747-8F and, so, will likely continue flying it for a couple more decades:

UPS (14)
AirBridgeCargo (7)
Silk Way Airlines (5)
Saudi Cargo (5)
Korean Air Cargo (7) (in addition to the 10 747-8Is operated by Korean Air)
Cathay Pacific Cargo (14)
Volga-Dnepr Airlines (5)
Atlas Air (10)
Nippon Cargo Airlines (8)
Cargolux (14)

Additionally, 8 747-8Is are being operated as business jets or VIP jets, not counting the 2 recently purchased by the U.S. Air Force for use as the next Air Force One fleet. If the past is any indication, the Air Force One 747-8s will likely still be in regular service (though technically not commercial service) even longer than most of the other recent 747 deliveries, due to the relatively low number of flight cycles that they get. They could possibly remain in service 30 years from now or more. For comparison, the current Air Force One fleet is composed of modified 747-200s, which have long been retired from airline service.

KLM are planning to retire their in 2020, pending delivery of replacement aircraft (if those are delayed, the fleet may of course remain in service a bit longer).

Quite a few, actually.
British Airways is the largest operator of B747-400 and flies a number of routes:

Where does the Boeing 747-400 fly?
The aircraft operates on a variety of routes, including:
Beijing  Boston Cape Town Dubai Lagos
Las Vegas Mexico Miami New York (JFK)
Phoenix San Francisco Toronto

Air China operates both 747-400s and 747-8s
KLM does so but is phasing the 747-400 out
Korean Air, Lufthansa, Thai Airways, Virgin, El Al, Saudia operate 747s, among others.
Wikipedia lists 489 747s in service as of July 2017 though around half of them are cargo and the numbers would have reduced still further by now.
The latest data that I could lay my hands on lists the following airlines (less than twenty, sadly):

Air China
Air India
Asiana Airlines
Atlas Air
British Airways
China Airlines
Corsair
El Al
Iraqi Airways
KLM Royal Dutch Airlines
Korean Air
Lufthansa
Mahan Air
Qantas
Rossiya Airlines
Thai Airways
Virgin Atlantic
Wamos Air

At first it looked like "Beijing - Boston - Cape Town - Dubai - Lagos" was one route that BA flies 747s on.

just like in good old days when they had the famous all around the world route :)
https://www.youtube.com/watch?v=Z1iOWJIdIRo&index=122

There are many airlines still operating the 747 in passenger service. Lufthansa has bought the 747-8, the last delivery was in April 2015, so I'd expect that the 747 will be in passenger service for at least another 20 years.
Here's your choice:

KLM
Lufthansa (both the Boeing 747-400 and 747-8)
British Airways
Thai Airways
Virgin Atlantic
Iran Air (747-200, probably the oldest passenger 747 still in commercial service)
China Airlines
Air China
Korean Air
Qantas
Air Atlanta Icelandic
El AL
Corsair
Dubai Air Wing
Saudi Airlines
Royal Air Maroc
Wamos Air
Rossiya Airlines
Atlas
Asiana
...

Probably more, but this is a start.

Air Atlanta Icelandic is a lessor and charter operation, right? Perhaps their most famous 747 is "Ed Force One," Iron Maiden's 747. It flies with the callsign "Atlanta 666."

I took this photo in July 2016 at the Frankfurt airport. So at least in 2016 Lufthansa did indeed operate Boeing 747.

These will keep on flying for a long time, since they're 747-8s, which entered service in 2012.

I flew a Lufthansa 747 in June 2018, though I think it was a -400, not a -8. Sadly, I didn't bother to look out the terminal window to see, nor do I remember from the seat back card. It was a lovely plane!

Looking at the older models, even the 747-200 is in commercial  use, here is a complete list. Some days ago a 747-200 of Fars Air Qeshm was damaged in an accident. Boeing is not allowed to deliver repair parts.
But mins asks actually about flying as passenger. I'm not sure, but a 747SP is some kind of 747-100? So it is maybe possible to fly as passenger with one from Las Vegas Sands. But I'm afraid you have to spend a lot of money.

Delta just retired their last 747, but plenty of others still use them. If you are in the Dallas area, you can see several 747's (mostly cargo, but BA operates the DFW->LHR->DFW route with a 747-400 - we call her "The Queen")


text:
What is the smallest manned jet aircraft?
In the movie Spy Kids (2001), there is a scene where the characters board a small jet aircraft "built for one passenger". The aircraft is about 2 meters tall with a 3 meters wingspan, and features a single jet engine, air intake located below the canopy, and tricycle landing gear.

Which got me wondering: what is the smallest fixed-wing jet-powered aircraft to date?
Some clarifications:

The aircraft must be able to takeoff and land under its own power (i.e. aircraft launched mid-air does not count).
The aircraft is propelled by one or more turbojet or turbofan engine(s) (i.e. no propellers, no rockets).
"Smallest" is measured by wing span.
The aircraft must be pilot operated (i.e. RC aircraft does not count).
This is not a question about whether an aircraft that small is possible, since there is already another very similar question. Rather, this question is about the smallest aircraft successfully flown in history to date.

That could be something like a coléoptère, if you focus on the wing span.

The title is a bit confusing. A UAV is still "pilot-operated". Perhaps "manned" is more appropriate.

+1 for giving a clear definition what "smallest" should mean.

I don't have a definitive answer, but the jet variant of the Colomban Cri-cri will probably be tough to beat. According to Wikipedia, its wingspan is 4.9 m (16 ft 1 in).

Probably a close second would be the Sonex Aircraft Subsonex, with an 18' wingspan.

Photo http://i.vimeocdn.com/video/538184554_1280x720.jpg

@RonBeyer - The BD-5J has a 17' wingpsan.

The BD-5J is what guinness world records claims to be the smallest but it is larger than the Cri-Cri in its jet implementation (the BD-5A is smaller than the Cri-Cri but prop powered)
If you want to count really experimental stuff the Martin Marietta X-24A lifting body has a wingspan of only 11 ft 6in. making it the smallest. Although I will admit it is predicated on a lose definition of "wing" and is rocket (not jet) powered.
Although if you broaden your definition of "aircraft" Yves Rossy's jet wing backpack is the smallest coming in at a wingspan of 7.9 ft. It is still piloted, jet powered although I do not think it can take off under its own power.

Great answer, but I think the BD-5A is a pusher prop. The jet variant is BD-5J.

@FredLarson Interesting, i did not know that ill modify to reflect. I see the 5B listed as a piston plane but cant really find much on the 5A

Second paragraph of the article: "The BD-5 has a small, streamlined fuselage holding its semi-reclined pilot under a large canopy, with the engine installed in a compartment in the middle of the fuselage, and a propeller-driving engine - or jet engine in the BD-5J variant"

Just found it hahah.

Also note the photo caption: "BD-5J N3038V, Guinness record holder for the world's smallest turbojet-powered manned aircraft."

I saw another article noting that as well. Its also what comes up if you search "smallest jet aircraft"

OP did say no rocket powered craft.  X-24A has a rocket engine.  Also, not sure it could take-off on its own - think it was always dropped.

The jet wing backpack was the first thing that popped into my mind, too. I discounted it for the same reason you did. Though I hear he's working on a version that can launch itself.

Neither of these seem to be able to take off under their own power

EM-10 Bielik has wingspan only 10 cm longer.

Regarding Yves' jetpack: in Britain it is not considered an aircraft but rather an aircraft component. As parts of Yves' body act as control surfaces he had to register himself as an airplane, though common sense prevailed and he was exempted from the seatbelt law.

I can attest that this is a hilarious little jet.  Saw Bob Bishop himself fly one at an airshow in the '90s sometime and got to meet him afterwards - talk about a guy with passion.  Given the number of these things that have killed their pilots you kind of have to be a bit mad to get into one.  Bishop himself later (luckily) managed to bail out of one that caught fire midair.  Canada lost our only BD-5 pilot about a decade ago when his wing fell off during flight practice in Ottawa.

BD-5J in action: https://www.youtube.com/watch?v=VlBUPtKIoHo

The Bede BD-5J is smallest according to Guinness.

Probably the best answer?  The Bell Rocket Belt.

Developed in the late 1960s, it used a Williams jet engine and could provide up to 20 minutes of flight at speeds as high as 85 mph.  The Army has evaluated it but eventually declined to purchase it and the project was dropped.


text:
How do fire crews handle hot brakes?
Let suppose an emergency aircraft has made an overweight landing. The brakes are white hot, and the fire crews are requested to be on scene.
What can be done about the hot brakes? Can they just shoot water at the gear assembly? If flames are visible, would they shoot foam instead?
This related question asks how do fire crew inspect the brakes, but not what they do when the brakes are known to be very hot.

Possible duplicate of When the brakes are checked, what do the firemen actually do?

Not duplicate, but related: How are brakes cooled on heavy aircraft?

One more vote on not dupe

I'm working on B747 cl. Here they used to use water when the temperature is close to 700°F, almost every time there is a wheel change the maintenance crew found the rotor brakes shattered like a crystal, but they continue doing it as a mean to not generate any cargo delay due to deflated wheel. Unsafe condition?
 Yes very much unsafe, a risk of a stuck wheel on takeoff or landing can occur.

Welcome to Aviation.SE. You say "they used to use" What do they do now? And who's "they"?


text:
Is this a Hurricane or Spitfire?
Can anyone identify the fighter here in this picture taken from a Dornier-do17?

From: https://stukablr.tumblr.com/post/145040185970/a-pic-took-it-from-a-donier-do17-a-hurricane

Note the link states its a hurricane.

Sadly, many a German airman's last words.

In addition to @qq jkztd's very good answer, I'd like to add that the Spitfire never had a such a wide oil radiator under the fuselage. That to me was the dead giveaway that it was a Hurricane. Quite a durable but honestly lackluster fighter.

Yes, all the silhouettes I can quickly find of Spitfires have the radiator under one or both wings, not under the fuselage.

Try looking at the illustration on the Spitfire Wikipedia page: all Spits had radiators under the fuselage, Hurricanes did not.

@TimLymington that is clearly false - https://en.wikipedia.org/wiki/Supermarine_Spitfire#/media/File:Spitfire_mk2a_p7350_arp.jpg vs https://en.wikipedia.org/wiki/Hawker_Hurricane#/media/File:Hurricane_in_planform_arp.jpg

@Jihyun But fairly well on par with the Do.17, designed around the same time. Also it was way easier and cheaper to build than a Spit, which was significant with wartime resources and serious technical problems with the Spitfire. Spitfires simply weren't ready in numbers by 1940.

Yes the small inlet there is for the carburetor air intake. It's really a simple matter of googling and checking various sources. And it's quite obvious. No radiator is that small XD. @Graham yes the Hurricane was sufficient for defense of the British Isles, but that was it. A point and shoot interceptor with little future except for limited recce and ground attack (which I admit it was adept at). I obviously have bias for the beautiful Spit.

@Jihyun Me too. :) But it's a bit like saying a Tornado wasn't a Jaguar, or an F-15 wasn't an F/A-18.  It was state of the art at the time it was designed, but it eventually became obsolete.

@TimLymington The small narrow central bulge under a Spitfire is the engine air intake and filter. The radiators were under the wings.

It's a Hurricane.  No Spitfire of any Mark had a radiator under the fuselage, whereas every Hurricane, from the prototype to the "Last of the Many" did.  And that is NOT a carburetor (carburettor in British English) air inlet.  Re the comment about the canopy, Mark I Spits had a narrow canopy.  No framed greenhouse, but not blown out at the sides either.  The earliest Mark I Spits had a canopy that effectively was just an extension of the windscreen.  Later ones had a bulged top for more head clearance, but still had flat sides.  Later Marks featured the "blown" canopy that was bulged on the sides as well.

Welcome to Av.SE!

It's a Hurricane. The radiator is on the fuselage, which means it is a Hurricane. On a Spitfire the radiator is on the right wing.

Agree with qq jkztd.
Also the canopy.  You can just about make out the lines (in profile, it looks like a greenhouse) plus it's narrower.  A Spit's is more bulbous.

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text:
What is this WW1 era plane?
I'm trying to identify this plane from an old family photograph.  Is it possibly  a DH4?

The tail number doesn't bring any success (well, at least not that I can find).
Any info would be much appreciated.

Any landing you can walk away from, eh?

We need a bit more info. Which country? What year? Any specific location?


text:
Why does an elevator deflection (step) result in a nonzero short-term-steady-state response in pitch rate?
I know from the simplified Short Period linearized equations (state space with Angle of Attack ($\alpha$) and Pitch Rate ($q$) as states) that the steady-state value of the pitch rate response to elevator deflection (step) is non-zero
I can also relate that to the spring-mass system and understand that the concise derivatives $M_{alpha}$ and $M_q$ work as spring and a damper, respectively.
I think (would appreciate confirmation) that the term short-term steady state should mean that the phugoid motion is going to take over eventually, being the dominant mode.
However, I would like to understand that physically, because $\alpha$ and $q$ seem to be both on steady state (impossible unless flight path changes). Also, I would expect $q$ to return to zero at some point. Does it mean this equation is oversimplified in this regard?

I think it would help a lot if you would post the actual state space model used. Is it actually a state space model with two states (pitch and pitch rate) or are there also states for e.g. velocity?

Actually, this applies to any general short period simplified representation. The velocity is assumed as constant for the mode and the system is represented in terms of α and q. To make it more clear, any system would have this same response, only varying according to the damping and frequency terms. What I need to understand is what is being left out so that this happens.

I mostly asked to see which states are part of your state spate representation; indeed, the actual system matrix does not really matter.

I see. I should've written: "...state space with Angle of Attack α and pitch rate q as the only states..."

Feel free to use the 'edit' button to improve your question. And of course, welcome to Aviation.SE!

The equation is certainly oversimplified, hence the name 'short period': it only models short period pitch oscillations. In this model, there are only two states: pitch and pitch rate. Any other effect is thus neglected.
A step response in an elevator would in the short term definitely lead to a nonzero pitch rate, as the model predicts. In reality, the pitch rate will usually decay to zero, because the airspeed drops to zero (there may also be altitude density effects). Imagine what would happen if you would pull on the stick in an aircraft, and crank the throttle to make sure the speed does not decay. You would do a vertical loop, exactly like the $q$ term predicts.
Of course, then you run in to an extra complication: your model is linearized. The concept of large angles, let alone a loop, does not exist in the linearized world. Think of a linearized pendulum: that works fine for small angles, but as far as the model is concerned, a 360° angle means just a very large deflection, and not the reality of returning to zero deflection after a full loop. The model is then only valid for the small amplitude oscillations it is intended to predict.
A phugoid mode exchanges speed for altitude and vice versa. Neither of these states are represented in  your short period linearized model. This behaviour is impossible to see in your model. You might as well ask why you don't see the effect of the Moon position in your model; it's simply not in the state space!
A long story short then: simplified models like these are great tools, but cannot and should not be used outside of what they are supposed to do. If you want to estimate instantaneous pitch rate from elevator deflection then this is the model for you. If you want to check for trim conditions, large attitude deviations, or even roll behaviour, then you need a better model.

Excellent answer! The only minor note is that the name 'short period' is not because the model is just 'oversimplified'. It rather happens that when we linearise the full model, for typical airplanes the states ɑ and q (in pitch) change much faster than the others (altitude and speed), and thus it makes (some) sense to analyse them separately - always, as you note, keeping in mind the limitations. But for very small airplanes, and particularly models, the frequencies are much closer, and it may become incorrect to consider 'short-period' motion for them separately at all.

@Zeus I meant to say that the name implies that it only predicts short-term effects and is invalid in the long run. Of course, the model was created with the reason to get a simple estimate of the short-term behaviour, not the other way round. Thanks for your comment.

Sorry, @Sanchises, my point was that the term short-period does not mean 'short term'! It means 'considering the states with quick response' (i.e. short period / high frequency). It is possible and valid to use a short-period-only linear model for quite a long stretch of time, as long as the conditions remain valid (V, H ~ const). For example, the airplane may exhibit pitch oscillations (being underdamped), while not departing the trajectory significantly. Or a simulator for the task of aiming a gunsight at a distant target might use a short-period model successfully.

I truly appreciate all the comments. I was afraid people would give replies on things I already knew and not address the real issue, but that second paragraph was exactly what I was looking for. Thanks!

@Zeus True. I was reasoning from the idea that the error dynamics are unstable when using the short-term model as an observer precisely because the conditions (the system matrix) do not remain constant in general. I will edit the answer to be a little bit more precise.


text:
How does the nozzle diameter affect the thrust of a ducted propeller?
I currently do some experiments with ducted propellers in which I try to figure out which effect a nozzle has on the thrust produced.
My theory goes like this: If I reduce the exit diameter of the duct the pressure is going to decrease and the air velocity and thus the thrust is going to increase. Consequently, you would want a small exit diameter.
However, in my experiments I measured the thrust of a 12x12 inch propeller at around 5500 rpm and got 20 N without a nozzle (just a constant diameter duct) and only 4 N with a nozzle reducing the exit diameter to 50 percent of the prop diameter.
These results are contrary to my theory! Does anybody have an explanation for this ? And what should I change to actually increase the thrust compared to the prop without a nozzle ?
Here are some pictures:

I would encourage you to get more results with various exhaust diameters, and, lengthening your duct so there is more distance between the fan and the exit.  Turbulence within the duct may be affecting the performance of your rotor.  Also, you may try a wide range of power settings.  Good data from this one!

Welcome. I'm afraid your theory wasn't actually working. Reducing the duct's exit diameter led to an increase in its internal pressure, increasing load on the propeller, and likely even causing some reverse flow.
Nozzle design is a complex subject. I can't think of a way to condense it, even limited to one specific case, into a suitable answer; maybe I don't get it enough myself. Keep that in mind; the below is just one small shard of the whole and by no means the full picture.
In general, the job of a nozzle is to match the pressure at jet engine exit to that outside it. If the pressure is different, it gets matched outside the engine, where it doesn't produce thrust.
When the engine is a rocket, which creates high pressure, the nozzle needs to expand the gas, converting pressure to thrust through acting on the nozzle. When the engine is a cold fan, which accelerates air, it's the opposite - the nozzle needs to compensate for the loss of pressure with a bit of compression, so that the air stream can exit without fighting the pressure of outside air at the back.
It's important for a convergent nozzle not to compress the exhaust to a higher pressure than the outside air, else it will destroy thrust. That was your case, the nozzle was too narrow, so it compressed the air to above ambient - which caused it to try and blow back through the fan.
To give a practical answer, an optimal nozzle at these velocities would be very similar to a simple duct, narrowing just a percent or two at the end, with a smooth exit shape.

Thanks for your answer! So do I get this right that after the propeller the air has a higher pressure than the air outside and the nozzle should narrow the duct just as much so that the pressure is equal to that outside the duct ? And because my nozzle decreased the diameter too much the pressure got too low and the jet had to "fight against the outside pressure" ?

Almost, but in reverse. The accelerated air has a lower pressure, but that pressure increases if there is an obstruction in the duct - like a convergent nozzle. In your case, the nozzle was far too narrow, so it pressurized the air to above ambient - and then it started pushing back against the air entering the propeller.

Ok, but doesn't the pressure decrease and the air accelerate when the diameter decreases ?

The pressure decrease happens in the obstruction and after it - it's increased by the obstruction, between the fan and the nozzle exit.

Ok so to sum it up: after the propeller the air has a higher pressure and velocity. The job of the nozzle is to convert some of that pressure into more velocity until the pressure matches the ambient pressure. If it continues narrowing though, the pressure increases again so the air eventually pushes back against the propeller decreasing the thrust ?

@SimonHenn no, without a nozzle you would have a lower pressure after the fan/propeller, not a higher one.

Why would I want a nozzle to lower the pressure then ? I‘d have to increase it, wouldn’t I ?

You just want the duct to maintain constant pressure throughout. If it's too narrow, the pressure rises aft of the propeller (imagine if the prop was blowing into a bucket, it would work as a weak compressor). If it's too wide, the pressure decreases. A very slight cone maintains constant pressure. Note that the result won't be very different from a straight duct.

This subject is one that the helicopter people have given a lot of thought. From this figure from Leishman we can see that the wake contracts by itself already.

The contracting shroud in your test setup has higher pressure just behind the propellor than at the shroud exhaust. This static pressure gradient exerts a force on the shroud area, resulting in negative thrust. Plus friction forces from the airstream in the duct.
The same book has a bit of a treatise on tail rotor fan-in-fin design based on momentum theory, which actually depicts a widening shape. More details in the masters thesis report, mentioned in this answer.

To add to @Therac's answer, you will probably add some drag on the outside of the nozzle by contracting it. The air flowing around it will separate if the contraction angle is too steep.
A bit of contraction makes sense, as the accelerated flow aft of the propeller will need less cross section for the given mass flow. You will also wish to make the capture area a bit larger than the cross section in the propeller plane. Just calculate the speed increase through the propeller disc and assume that half of that is reached in the propeller plane. This will ensure that pressure is about constant along the whole duct and losses are minimized.

The thrust equation gives us Thrust =  Mass x Acceleration
You increased the airspeed but reduced the airflow.

Ok thanks for your answer! But doesnt the airspeed increase so that the same mass of air can get through the pipe ?

This is great work, and you are off to a good start.  You may wish to review jet engine design. What you are building seems to be the compressor half.  Narrowing the "exhaust end" will increase pressure in the duct, which is what you want a compressor to do.  Forward motion created when applied to an aircraft will add to this affect. This could  be an air "scoop" for a piston engine!
The best way to test your designs might be full throttle in level flight, as this would also give you nacelle drag data.  Top speed comparisons will probably show by far a properly pitched prop with no duct will win the power to thrust efficiency test, but not without much being learned.
Ducted fans look great on scale model designs, but generally drain the batteries much
faster than props.  They do have advantages at very low or hovering speeds, but props take over from around 50 to around 400 mph.
I would definitely continue this work for application of boosting power in piston engines.
Sports cars have air scoops on their hoods, this one might be better.

At subsonic speeds, velocity increases with decreasing cross-sectional area and static pressure decreases.